It is known that enzymes can be immobilized without using a carrier by cross-linking with polyethylene imine (PEI) and a cross-linking agent such as glutaraldehyde or polyazetidine (e.g. U.S. Pat. No. 4,288,552, U.S. Pat. No. 4,355,105, EP 297,912). Such methods can be used to produce immobilized enzymes in particle form with good activity and physical strength, suitable for continuous use in a fixed-bed column. However, PEI is an expensive material, so it is desirable to find alternatives to this. Also, immobilization of some enzymes with PEI some times leads to poor flocculation, resulting in difficult dewatering.
It is the purpose of the invention to provide a method with improved flocculation and dewatering and without the need for PEI for producing an immobilized enzyme preparation with satisfactory properties for fixed-bed column use: activity, stability (half life) and physical strength (pressure drop).